Draft gear assemblies which utilize friction-type clutch mechanisms to absorb heat energy generated during service have been in widespread use on railway cars for several years prior to the present invention, as is generally well known in the railway art. These draft gear assemblies are disposed within an elongated opening located in the center sill member of the railway car along the longitudinal axis thereof and behind the shank, or innermost end, of the railway car's coupling mechanism. In this position, these friction clutch type draft gear assemblies will absorb at least a relatively large portion of both the buff and draft forces generated during service. Such buff and draft forces encountered by such railway car are usually being applied in an alternating manner to the center sill member during normal car operation on the track.
A representative teaching of such prior art type friction clutch draft gear assemblies can be found, for example, in U.S. Pat. Nos. 2,916,163; 3,178,036; 3,447,693; 4,576,295; 4,645,187 and 4,735,328. Most, if not all, of these prior art type draft gear assemblies either have been or still are being utilized in the railway industry prior to the development of the present invention. Furthermore, except for U.S. Pat. Nos. 4,576,295 and 4,735,328, each of the remaining above-identified patents is owned by the assignee of the present invention. The teachings of each of the above-referenced patents are incorporated herein by reference thereto.
It is quite well recognized, by those persons who are skilled in the friction clutch type draft gear assembly design art, that these draft gear assemblies must be provided with the capability of maintaining at least a certain minimum shock absorbing capacity both during making up a train consist and in-track service. Such minimum capacity has been specified by the Association of American Railroads (AAR) and is defined in the standards issued by the AAR. For example, friction clutch type draft gear assemblies have a specified absolute minimum capacity rating of at least 36,000 foot pounds. Any draft gear assembly with a capacity rating which is determined to be below 36,000 pounds will not receive approval from the AAR for service on any railroad car which may be used in interchange.
It is, likewise, important to note that the heat energy absorbing action of the friction clutch mechanism must enable this minimum capacity rating to be readily achieved without exceeding a specified maximum 500,000 pound reaction force, or pressure, being exerted on the center sill member of the railway car during both such make-up and operation of such train consist. It has been found that such maximum reaction pressure is required to enable these high energy shocks to be readily absorbed without upsetting the end of the coupling member shank and/or damaging other critical car components and/or the lading that is being transported by such railway car.
In order for the manufacturers of such friction clutch type draft gear assemblies to meet the requirements of the railroad industry, with the ever increasing load carrying capacity of their modern day railroad cars, it has become of extreme importance to enhance the overall rated capacity of the friction-type draft gear assemblies as much as possible. This higher capacity rating being found necessary in order to minimize any damage to such cars and/or the lading due to the increased forces being exerted on the center sill member of the cars by the heavier loads such cars are now carrying.